Antigens and immunogenicity

Question 1

What is an immunogen? What is an antigen?

Answer 1

antigen –> anything that is recognized by anti-bodies OR can be degraded into peptides and recognized by T cells when bound to MHC receptors.

Immunogen –> antigens that will elicit an immune response

essentially an antigen is something that can be detected by our ADAPTIVE IMMUNE response

Question 2

t or f, all immunogens are antigens but not all antigens are immunogens

Answer 2

true,

all immunogens are antigens not vice versa.

Question 3

what is an epitope?

Answer 3

the location on an antigen that is bound to an antibody or T cell receptor.

epitope = antigenic determinant

Question 4

what is the an Fc region and an Fc receptor?

Answer 4

Fc region is a part of the conserved region on a antibody. Typically, antibodies bind to an antigen and then this the Fc region binds to a macrophage Fc receptor for phagocytosis (opsonization)

Question 5

true or false, T cells have T cell receptors which bind antigens.

Answer 5

true.

antibodies can bind antigen epitopes and so can T cell receptors on T cells.

Question 6

what is an antigens valency?

Answer 6

the number of antigenic determinants (epitopes) found on the antigen. Most antigens are multivalent.

Question 7

what is a b cell receptor (BCR)?

Answer 7

this is a B cell membrane bound antibody.

antibodies can either be membrane bound or secreted

Question 8

what is an antibody valency? compared to antigen valency?

Answer 8

antibody –> how many epitopes / antigenic sites it can bind too

antigen –> how many epitopes it has.

Question 9

what is the valency of a monomeric antibody?

Answer 9

2

Question 10

what is a T cell receptor (TCR) ?

Answer 10

TCR’s are expressed on the membranes of T cells similar to BCR’s on B cells.

TCR’s recognize the MHC (major histocompatibility complex) receptor of an antigen presenting cell

Question 11

t or f, antigens can be detected by TCR’s

Answer 11

false, antigens must be presented on MHC receptors and T cell receptors recognize this complex

Question 12

what is immunodominance?

Answer 12

many antigens are multivalent in which case they have many epitopes for antibodies to bind too. Some of these epitopes may elicit a much stronger immune response (such as much more antibodies are produced for a particular epitope). This epitope is then immunodominant.

Question 13

what is the difference between sequential and non-sequential epitopes?

Answer 13

an antibody can bind two epitopes side by side –> sequential.

sometimes however, they are not near each other. sometimes the peptide is folded a bunch and the epitopes are nearby only due to foldings. This is aka discontinuous epitopes.

Question 14

what is antibody epitope accessibility?

Answer 14

this refers to how the epitopes are connected and how easily an antibody can bind them.

Question 15

explain HIV and its accessibility.

• spike proteins
• glycan shield
• mutations

Answer 15

spike proteins are neccessary for HIV to get into organisms. However they are immunogenic. Therefore antibodies can bind these regions and neutralize the virus.

however, the tip of spike proteins are variable and allow the virus to mutate and evade.

also, HIV has a glycan layer shield which inhibits many antibodies from interacting with its epitopes.

Question 16

What is HIV’s membrane proximal external region (MPER) ?

Answer 16

this is a conserved region on the outside of HIV unlike spike proteins. conserved means no mutation therefore good cure target.

Question 17

how does antibodies bind antigen epitopes?

Answer 17

NON - COVALENTLY!!

• electrostatics
• H bonds
• Van der Waals
• hydrophobic forces

Question 18

explain how foreignness can affect immunogenicity

Answer 18

foreigness –> the more distant two molecules are in terms of phylogentics, the more likely one molecule will cause an immune response.

Question 19

what are 
isogenic / autologous 
syngenic
allogenic
xenogenic

Answer 19

isogenic / autologous = self
syngenic = same, e.g. twins
allogenic = same species
xenogenic = different species

top to bottom = increasing immunogenicity

Question 20

what would we get more of an immune response from?

chicken albumin or monkey albumin?

Answer 20

chicken since its a much further relative

Question 21

explain how molecular size can effect immunogenicity .

Answer 21

molecular size –> molecules with a mass over 10kDa are good immunogens (cause immune reaction) .

bigger elicits more immune response

Question 22

what is serum sickness?

Answer 22

allergic reaction to foreign proteins / molecules within an injected serum. Often this serum is an anti-venom or something that is countering an effect.

e.g. get small amount of venom, inject in someone, develop antibodies. Next “case” of a bite, use this new vaccine. The individual can get serum sickness from this anti-venom since its foreign.

Question 23

What is a hapten?

Answer 23

a hapten is an antigenic molecule that is NOT immunogenic by itself.

i.e. this is a case of when an antigen is not an immunogen

(recall all immunogens are antigens)

Question 24

how does a Hapten become an immogen?

Answer 24

it must bind some sort of host carrier. some poisons must bind a plasma protein. Then this complex is recognized as foreign.

often haptens are very small

Question 25

what is an adjuvant?

Answer 25

this is a molecule that is not immunogenic on its own. However, when injected with an antigen, adjuvants will enhance the immune response.

these are often used to aid in vaccine immune responses.

Question 26

why are adjuvants injected with vaccines?

Answer 26

the purpose of a vaccine to acquire adaptive immunity that your body can remember. To do this it must mount a primary immune response first. Sometimes the injured pathogen can’t elicit enough of a response and therefore adjuvants are used to enhance the initial response.

Question 27

how does biological systems influence the immune response?

Answer 27

• need to be genetically fit (not immunocompromised)

- need enough exposure to the pathogen for immunity

Question 28

influencing the immune response. Due to the “route of exposure” where is the immune response most found.

• subcutaneous / IM
• IV
• nasal / oral

Answer 28

• subcutaneous / IM –> draining lymph node response
• IV –> systemic response and lots of spleen action
• nasal / oral –> mucosal response